Superconducting quantum circuit device and control method

Abstract

Provided are: a superconducting quantum circuit device capable of freely switching between operating in four-body interaction and operating in three-body interaction without changing the circuit structure of a superconducting quantum circuit; and a control method for the superconducting quantum circuit. The present invention comprises: first through fourth quantum bits; a coupler that is provided with a loop circuit including a plurality of Josephson junctions and is coupled to the first through fourth quantum bits; and a control means that switches between a first operation mode in which the first through fourth quantum bits perform four-body interaction through the coupler, and a second operation mode in which three quantum bits excluding one of the first through fourth quantum bits perform three-body interaction through the coupler. The control means is provided with a magnetic field generation unit that generates a magnetic field to be applied to the loop circuit, and a control unit that changes the intensity and / or frequency of the magnetic field.

Description

Superconducting quantum circuit device and control method

[0001] The present disclosure relates to a superconducting quantum circuit device and a control method.

[0002] Quantum annealing is a method for solving combinatorial optimization problems, and one of the quantum annealing methods is called the LHZ (Lechner, Hauke, Zoller) method. To physically implement the LHZ method, it is necessary to realize a quantum bit, which is a basic element, and a network thereof, in particular a network in which four quantum bits interact simultaneously (four-body interaction) (Patent Document 1).

[0003] International Publication No. 2017 / 001404

[0004] Shruti Puri, et. al., "Quantum annealing with all-to-all connected nonlinear oscillators", Nature Communications 8, 15785 (2017)K. Ender, et. al., "Parity Quantum Optimization: Compiler", Quantum 7, 950 (2023)

[0005] Depending on the problem to be handled by quantum annealing, the problem can be solved more efficiently if three-body interactions can be utilized in addition to four-body interactions (Non-Patent Document 2).

[0006] One of the objects of the present disclosure is to provide a superconducting quantum circuit device that can freely switch between operation with four-body interactions and operation with three-body interactions without changing the circuit structure of the superconducting quantum circuit, and a method for controlling a superconducting quantum circuit.

[0007] In one aspect of the present disclosure, a superconducting quantum circuit device includes first to fourth quantum bits, a coupler including a loop circuit including a plurality of Josephson junctions and coupled to the first to fourth quantum bits, and further includes control means for switching between a first operating mode in which the first to fourth quantum bits perform four-body interactions via the coupler and a second operating mode in which three quantum bits, excluding one quantum bit, of the first to fourth quantum bits perform three-body interactions via the coupler. The control means includes a magnetic field generation unit that generates a magnetic field to be applied to the loop circuit, and a control unit that changes the strength and / or frequency of the magnetic field.

[0008] In another aspect of the present disclosure, a method for controlling a superconducting quantum circuit comprising first to fourth quantum bits and a coupler comprising a loop circuit including a plurality of Josephson junctions and coupled to the first to fourth quantum bits includes a first operating mode in which the first to fourth quantum bits undergo four-body interactions via the coupler, and a second operating mode in which three quantum bits, excluding one of the first to fourth quantum bits, undergo three-body interactions via the coupler, and switches between the first operating mode in which the circuit operates using the four-body interactions and the second operating mode in which the circuit operates using the three-body interactions by applying a magnetic field to the loop circuit and changing the strength and / or frequency of the magnetic field.

[0009] According to the present disclosure, it is possible to realize a device that can freely switch between operation based on four-body interactions and operation based on three-body interactions without changing the circuit structure of the superconducting quantum circuit.

[0010] FIG. 1 is a diagram schematically illustrating an example of a superconducting quantum circuit according to the present disclosure. (A) and (B) are diagrams illustrating an example of a SQUID and a coupler according to the present disclosure. (A) and (B) are diagrams illustrating the present disclosure. (B) are diagrams illustrating the strength of coupling of a three-body interaction according to the present disclosure. (B) are diagrams illustrating the strength of coupling of a four-body interaction according to the present disclosure. (A) and (B) are diagrams illustrating an example of a coupler according to the present disclosure. (B) are diagrams schematically illustrating an example of a coupler according to the present disclosure. (B) are diagrams schematically illustrating an example of the configuration of a superconducting quantum circuit device according to the present disclosure. (B) are diagrams schematically illustrating an example of the configuration of a superconducting quantum circuit device according to the present disclosure. (B) are diagrams schematically illustrating a quantum computer according to the present disclosure.

[0011] In a superconducting quantum circuit in which first to fourth quantum bits perform four-body interactions via couplers, it would be useful to realize an efficient LHZ system if three-body interactions could also be realized without changing the circuit structure, while maintaining the same circuit structure as for the four-body interactions. When a Josephson parametric oscillator (JPO) is used as a quantum bit as one implementation format of the LHZ system, four-body interactions can be realized, but three-body interactions are not considered.

[0012] The above problem is one example, but the present disclosure is not limited to the above problem. It proposes a completely new technique (configuration and method) that makes it possible to realize three-body interactions simply by changing the setting parameters, without changing the circuit structure of four-body interactions.

[0013] The operating principle of the superconducting quantum circuit proposed in this disclosure will be outlined with reference to Fig. 1. Below, an example in which a quantum bit is configured using a Josephson parametric oscillator (JPO) will be described. The superconducting quantum circuit includes first to fourth JPOs and a coupler (21) that capacitively couples to the first to fourth JPOs. The coupler (21) has a loop circuit (10) including multiple Josephson junctions.

[0014] In the first operation mode, the first to fourth JPOs perform four-body interactions via the coupler 21. By providing a DC signal (DC current) as a control signal to the coupler 21, a DC magnetic field is applied to the loop circuit 10 of the coupler 21, and AC signals (microwave signals) are provided as pump signals to the first to fourth JPOs, resulting in the resonance angular frequencies ω of the first to fourth JPOs. ｉ (i = 1 to 4) is the four-body interaction condition (ω １ +ω ２ =ω ３ +ω ４ The pump signal is set to satisfy the resonant angular frequency ω ｉ The angular frequency is set to be approximately twice the frequency of the

[0015] In the second operation mode, an AC magnetic field is applied to the loop circuit (10) of the coupler (21), and the oscillation frequency of the magnetic field applied to the loop circuit (10) is set to a resonance angular frequency ω ｋ The first to fourth JPOs (JPO1 to JPO4) are set to have a resonant angular frequency (ω) of one JPOk that is not involved in the three-body interaction, and three JPOs, excluding one JPOk, among the first to fourth JPOs, are set to have a resonant angular frequency (ω) of one JPOk that is not involved in the three-body interaction, as a control signal given to the coupler (21). ｋ ) (k is 1 to 4) ｇ，ｐ =ω ｋ For example, if one JPO removed from the four-body interaction is JPO4, then ω １ +ω ２ =ω ３ +2ω ｇ，ｐ This becomes:

[0016] The resonant angular frequency is used as a pump signal for JPOk that does not participate in three-body interactions, and the resonant angular frequency (ω ｋ ) and a different frequency (ω ｋ’ For example, if one JPOk removed from the four-body interaction is set as JPO4, then ω １ +ω２ ≠ω ３ +ω ４’ That is, the resonance angular frequencies of the first to fourth JPOs are set so as not to satisfy the condition of four-body interaction.

[0017] As described above, by controlling the coupler (21) and the JPO, the first and second operating modes can be freely switched by changing the parameters set for each quantum bit (JPO) and the coupler, without changing the circuit configuration.

[0018] The loop circuit (10) of the coupler (21) has n (n is a positive integer of 2 or more) first Josephson junctions (JJ1) spaced apart from each other and arranged in series, and a second Josephson junction (JJ2) arranged in parallel with the n first Josephson junctions. The second Josephson junction has a junction size (Josephson energy) smaller than the junction size (Josephson energy) of the first Josephson junction.

[0019] An example of the configuration of a superconducting quantum circuit 1 in the present disclosure will be described in detail with reference to Fig. 1. The superconducting quantum circuit 1 includes four quantum bits: JPO1 (20A) to JPO4 (20D), and a coupler 21. JPO1 (20A) to JPO4 (20D) are capacitively coupled to the coupler 21 via coupling capacitors 31A to 31D, respectively. In the following, an example in which each JPO is a lumped constant type will be described, but it goes without saying that each JPO may also be a distributed constant type.

[0020] JPO1 (20A) to JPO4 (20D) each include: SQUIDs (SQUID loops) 210A to 210D in which first superconducting portions 203A to 203D, first Josephson junctions 201A to 201D, second superconducting portions 204A to 204D, and second Josephson junctions 202A to 202D are connected in a ring; magnetic field generating units 207A to 207D each consisting of a line (inductor) that is inductively coupled to the SQUID loops 210A to 210D and that generates a magnetic flux that penetrates the SQUID loops 210A to 210D by passing a pump signal that is supplied to control lines 23A to 23D from a signal generating unit (not shown); and capacitors 206A to 206D connected between the first superconducting portions 203A to 203D and the second superconducting portions 204A to 204D.

[0021] The second superconducting portions 204A to 204D of JPO1 (20A) to JPO4 (20D) are connected to ground.

[0022] The coupler connection parts 24A and 24B connected to the first superconducting parts 203A and 203B of JPO1 (20A) and JPO2 (20B) are connected to the first and second opposing parts 17A and 17B of the coupler 21 via coupling capacitors 31A and 31B, respectively.

[0023] The coupler connection parts 24C and 24D connected to the first superconducting parts 203C and 203D of JPO3 (20C) and JPO4 (20D) are connected to the third and fourth opposing parts 19A and 19B of the coupler 21 via coupling capacitors 31C and 31D, respectively.

[0024] The coupler 21 comprises: a loop circuit 10 connected to one end 16 (first electrode) and the other end 18 (second electrode) of the coupler 21 and including a plurality of Josephson junctions (JJs); and a capacitor 15 connected in parallel to the loop circuit 10.

[0025] More specifically, the loop circuit 10 includes: n first Josephson junctions 11-1 to 11-n connected in series and spaced apart from one another between one end (first electrode) 16 and the other end (second electrode) 18 of the coupler 21; and a second Josephson junction 12 connected in parallel with the first Josephson junctions 11-1 to 11-n between the one end (first electrode) 16 and the other end (second electrode) 18 of the coupler 21.

[0026] The magnetic field generating unit 14 is composed of a line (inductor) that is inductively coupled with the loop circuit 10 of the coupler 21, and flows a DC signal that is supplied to the control line 13 of the superconducting quantum circuit 1 via a coaxial cable (not shown) or the like from a signal source (current control unit) (not shown) arranged outside the dilution refrigerator (not shown), and generates a magnetic flux Φ g The magnetic field generating unit 14 may be a coplanar superconducting line or a superconducting coil, one end of which is connected to the control line 13 and the other end of which is connected to the ground.

[0027] 1, the n first Josephson junctions 11-1 to 11-n connected in series are connected so that the ends of the (n+1) adjacent superconducting lines overlap, and the n overlapping portions are formed by tunnel junctions of (one end of a superconducting line) / (insulating film) / (one end of an adjacent superconducting line). The other ends of the first and (n+1)-th superconducting lines are connected to one end (first electrode) 16 and the other end (second electrode) 18 of the coupler 21, respectively.

[0028] The coupler connection parts 24A and 24B of JPO1 (20A) and JPO2 (20B) are capacitively coupled to one end (first electrode) 16 of the coupler 21. The coupler connection parts 24C and 24D of JPO3 (20C) and JPO4 (20D) are capacitively coupled to the other end (second electrode) 18 of the coupler 21. That is, in FIG. 1, the first and second opposing portions 17A and 17B connected to one end (first electrode) 16 of the coupler 21 are capacitively coupled to the coupler connection portions 24A and 24B of JPO1 (20A) and JPO2 (20B) via coupling capacitors 31A and 31B, respectively, and the third and fourth opposing portions 19A and 19B connected to the other end (second electrode) 18 of the coupler 21 are capacitively coupled to the coupler connection portions 24C and 24D of JPO3 (20C) and JPO4 (20D) via coupling capacitors 31C and 31D, respectively.

[0029] The capacitance of the capacitors 206A to 206D of JPO1 (20A) to JPO4 (20D) is C Ｊ , the capacitance of the capacitor 15 of the coupler 21 is C ｇ , and the capacitance of the coupling capacitors 31A to 31D is C.

[0030] 2A, in the SQUID, the first Josephson junction 11 is a portion (tunnel junction) where the ends of superconducting lines 101-1 and 101-2 are in contact with each other via an insulating film (oxide film), and the second Josephson junction 12 is a portion (tunnel junction) where the ends of superconducting lines 102-1 and 102-2 are in contact with each other via an insulating film (oxide film). Superconducting lines 103 and 104 connected to the superconducting lines 101-1 and 102-1 and the superconducting lines 101-2 and 102-2, respectively, may be made of the same superconducting material as the superconducting lines 101-1 and 102-1 and the superconducting lines 101-2 and 102-2, or may be made of different superconducting materials.

[0031] The SQUID loop in Figure 2(A) is a magnetic flux Φ g When the phase difference between the first and second Josephson junctions 11 and 12 is φ １ , φ ２ and ignoring the linear inductance of the superconducting line, the following holds: (1)

[0032] In equation (1), Φ ０ is the magnetic flux quantum. (2) Here, h is Planck's constant (approximately 6.6×10^(-34) joule-seconds) and e is the elementary charge (approximately 1.6×10^(-19) coulombs).

[0033] According to equation (1), (3)

[0034] The potential energy V(φ) of the SQUID loop in FIG. １ ) is given by the following equation (4): (4)

[0035] In formula (4), E Ｊ１ , E Ｊ２ are the Josephson energies of the first and second Josephson junctions 11 and 12. (5) I C,i (i=1, 2) is the critical current of the first Josephson junction 11 and the second Josephson junction 12. The critical current of the Josephson junction is proportional to the junction size of the Josephson junction, for example, and from equation (5), the Josephson energy is also proportional to the junction size of the Josephson junction.

[0036] FIG. 2B is a diagram illustrating the coupler 21 of FIG. 1. The loop circuit 10 includes an array of n first Josephson junctions 11-1 to 11-n connected in series and spaced apart from one another between nodes n1 and n2, and a second Josephson junction 12 connected in parallel to the array. The n first Josephson junctions 11-1 to 11-n connected in series and spaced apart from one another are, for example, tunnel junctions where the ends of a pair of adjacent superconducting lines, for n+1 superconducting lines 101-1 to 101-n+1, ​​are in contact with each other via an insulating film (oxide film). The superconducting lines 101-1 and 101-n+1 are connected to superconducting lines 103 and 104, respectively. The superconducting lines 103 and 104 may form first and second electrodes 16 and 18. The second Josephson junction 12 is a portion (tunnel junction) where the ends of the superconducting lines 102-1 and 102-2 contact each other via an insulating film (oxide film), as in FIG. 2A.

[0037] For an array of n first Josephson junctions 11-1 to 11-n connected in series, the phase difference between both ends of the array (between nodes n1 and n2) is φ １ and the phase difference at the second Josephson junction 12 is φ ２ Then, the above formula (3) is established. The phase difference φ between both ends of the array of the first Josephson junctions 11-1 to 11-n is １ The phase difference φ / n obtained by equally dividing the above is defined as the phase difference between the input and output of each of the Josephson junctions 11-1 to 11-n. The potential energy of the n first Josephson junctions 11-1 to 11-n connected in series is calculated by dividing the potential energy of each of the n first Josephson junctions 11-1 to 11-n by the following formula: (6) is given by adding n times. (7)

[0038] However, the above formula (7) is based on the Josephson energy E Ｊｇ is the charging energy E Cand the capacitance between the array of the first Josephson junctions 11-1 to 11-n and the ground is sufficiently smaller than the capacitance of the first Josephson junction 11 (Reference 2, Reference 3, etc.).

[0039] The loop circuit 10 in FIG. 2B is connected to a magnetic flux Φ g When penetrated, the potential energy is (8)

[0040] Here, in the case of four-body interaction, the magnetic flux Φ penetrating the loop circuit 10 ｇ of (9) (DC bias).

[0041] Therefore, equation (8) becomes the following equation (10).

[0042] (10)

[0043] In the loop circuit 10 of the coupler 21, the junction size of the second Josephson junction 12 is smaller than the junction size of the first Josephson junction 11, and E Ｊ１ = E Ｊｇ , E Ｊ２ = αE Ｊｇ (where 0 < α < 1) (11)

[0044] 3 is a diagram for explaining the three-body interactions in the four JPO1 (20A) to JPO4 (20D) described with reference to FIG. 1. Note that the magnetic field generating units 207A to 207D in FIG. 1 are not shown in FIG. 3. In FIG. 3, magnetic fluxes φ1 to φ4, φg1, and φg2 are placed at the nodes 1 to 4, g1, and g2, respectively (see, for example, Reference 2, etc., for the fluxes (magnetic fluxes) placed at the nodes). １ ~Φ ４ represents the magnetic flux passing through each SQUID loop. Ｊrepresents the Josephson energy.

[0045] When the coupler 21 is operated as a three-body interaction coupling, a fixed magnetic flux Φ (0) g (e.g., Φ / 2) plus a predetermined angular frequency ω p,g Oscillating magnetic field εcos(ω p,g That is, the magnetic field applied to the loop circuit 10 is given as Φ (0) -g (=Φ0 / 2=h / (4e)), amplitude ε(Φ0 / (2π)), angular frequency ω p,g Vibrate with. (12)

[0046] In this case, in equation (8), is φ １ φ ｇ＿ Then, from equation (12), The potential energy of the coupler 21 is V ｇ is the phase difference between the superconducting currents at both ends (nodes g1 and g2) of the coupler 21. ｇ＿ is expressed as a function of the following equation (13):

[0047] (13)

[0048] Here, first, when ε = 0 (Φ ｇ （ｔ） =Φ （０） ｇ (When) (14)

[0049] The realized state is V ｇ The minimum point φ min g- For example, n, α, Φ （０） ｇ In order to have one minimum point, it can be determined by -π≦φ min g - <π (15) α<1 / n (16)

[0050] Expression (14) is the minimum point φ ming- By Taylor-expanding up to the fourth order around φg_ and ignoring the sixth and subsequent orders of φg_, the following equation (17) is obtained (at the minimum point φ min g- (The coefficient of the first-order term at 1 is 0). (17)

[0051] In equation (17), the coefficient E of the m-th order term （ｍ） Ｊｇ Also, n, α, Φ (0) g , and φ min g- is determined by.

[0052] In the following, Φ (0) g =Φ0 / 2 (this is called quarton-like type). In this case, in the range of α<1 / n, φ min g- =0.

[0053] Also, Φ g (t)=Φ (0) g =Φ0 / 2 and assume the following potential:

[0054] (18)

[0055] where: (19)

[0056] When ε≠0, the vibration amplitude ε is, for example, (20) is satisfied. For example, Φ (0) g When =Φ0 / 2, 0 < ε << π (ε is a positive value that is much (sufficiently) smaller than π).

[0057] In equation (13), the magnetic field Φ with ε as a coefficient ｇ The vibration term of (t) is assumed to vibrate in the GHz (gigahertz) band, for example. In this case, the realized state is the minimum point (φ g- =0).

[0058] Regarding equation (13), taking into account the first-order terms of the vibration amplitude (parameter) ε, Vg(φ g- ) to φ g- =0 (=φ min g- ) and develops around it.

[0059] (twenty one)

[0060] where: (twenty two)

[0061] φ ｇ- Note that the odd-order coefficients are the first-order terms of the angular frequency ω ｐ，ｇ The even-order coefficients are the same as in equation (18) and are time-independent. The frequency of the third-order coefficient and the JPO pump angular frequency ω ｐ，ｇ When one JPO that does not participate in the three-body interaction is JPO4(20D), ω1+ω2=ω3+2ω g,p　　　　　　 (23)

[0062] 3 is a simplified diagram of the circuit configuration of FIG. 1, and is a circuit diagram for explaining the derivation of the Hamiltonian of the superconducting quantum circuit. The Hamiltonian of the circuit shown in FIG. 3 is obtained, and the coupling coefficient g （３） Ask about.

[0063] Following standard techniques (e.g., Ref. 2), we develop a classical Hamiltonian for the circuit of FIG.

[0064] (twenty four)

[0065] In formula (24), C mat -１ is the capacitance connection matrix (6 rows and 6 columns) C mat is the inverse matrix of (twenty five)

[0066] (26) t represents transposition.

[0067] The coordinate φ and momentum q are the creation and annihilation operators a ＋ , a, the Hamiltonian is quantized using the phase φ ｋ and the number of bosons (Cooper pairs) n ｋ =q ｋ / 2e (k=1,2,3,4,g1,g2) is quantized using boson creation and annihilation operators.

[0068] (27)

[0069] (28)

[0070] where: (29)

[0071] (30)

[0072] In the formulas (29) and (30), (31)

[0073] (32)

[0074] In formula (31), E Ｃ is the capacitor C Ｊ In the formula (32), E' Ｃｇ is the capacitor C of the coupler 21 ｇ represents the effective energy that takes into account the effect of bonding with JPO in the charging energy of

[0075] a ＋ ｋ and a ｋ (k=1,2,3,4,g1,g2) are the boson creation and annihilation operators. The coupler 21 has two flux degrees of freedom φ ｇ１ , φ ｇ２ There is.

[0076] ^φ k and ｋ , a ｋThe following operators are defined for (k=g1, g2). (33) (34) (35)

[0077] In formula (33), (36)

[0078] In formula (34), (37)

[0079] Z in Equation (36) and Equation (37) ｇ is given by: (38)

[0080] JPO ｉ Magnetic flux Φ passing through each SQUID loop (i=1,2,3,4) ｉ A pump wave (microwave) of angular frequency ωp,i is applied so that the following holds true: (39)

[0081] The quantized Hamiltonian H Ｑ is expressed by the following equation (40). (40)

[0082] In formula (40), g ＋ and g － is the strength of interaction between each JPO and the two degrees of freedom of the coupler 21. Also, in equation (40), s １ =s ２ = 1, s ３ =s ４ = -1 (41).

[0083] In formula (40), H JPO,i Each JPO ｉ (i=1,2,3,4) Hamiltonian. (42)

[0084] Here, ω is the resonant angular frequency of each JPOi (i=1 to 4) (the resonant angular frequency corresponding to the boson operator ai), and is given by the following equation (43). (43)

[0085] E in formula (42) ｃ is the capacitance C of each JPOi (i = 1 to 4) Ｊ is the charging energy. (44)

[0086] In equation (40), for convenience of notation, the following is defined as the Hamiltonian H of the coupler 21: coupler It states that: (45)

[0087] In formula (45), E ’ ｃｇ is the combined capacitance: C ｇ +C charging energy, given by the following formula: (46)

[0088] In equation (45), ω － , ω ＋ is the resonant angular frequency of the coupler 21 (boson operator a ｇ－ , a ｇ＋ where the difference in angular frequency between different JPOs is not taken into account. (47)

[0089] (48)

[0090] Since each JPO interacts with the coupler 21, it is thought that the JPOs also indirectly interact with each other through their interactions with the coupler 21. If a variable transformation is performed to incorporate the influence of the coupler 21 into each JPO, the interactions between JPO1 to JPO4 and the coupler 21 are transformed into four-body interactions between the JPOs. In other words, the Hamiltonian can be transformed into one in which the JPOs interact directly with each other. This transformation is expressed as a unitary transformation using the unitary matrix U, as shown in the following equation (49):

[0091] (49)

[0092] where: (50) (51)

[0093] g in formula (50) ＋ and g in equation (51) － is given by: (52)

[0094] (53)

[0095] In addition, g' ＋ = g ＋ / (ω-ω ＋ ), g'_=g － / (ω-ω － ) is less than 1.

[0096] After performing the unitary transformation, the bosons ai of each JPOi are transferred to a rotating coordinate system. (54)

[0097] The rotation frequency of the coordinate system is different for each JPO. The pump angular frequency ω applied to JPOk (k=1 to 4) ｐ，ｉThe JPOk (k = 1 to 4) is represented in a coordinate system rotating at half the frequency of the pump signal that generates the magnetic flux passing through the loop of the SQUID (201A to 201D). The pump frequency is different for each JPO. By shifting to the rotating coordinate system, time-oscillating terms appear in the quantized Hamiltonian HQ. These oscillating terms are averaged over the time scale of interest, and their positive and negative values ​​cancel each other out. Therefore, they can be ignored (rotating wave approximation). Due to the difference in pump frequency between each JPO, many of the terms representing the interactions between the JPOs and between the JPO and the coupler 21 oscillate. Therefore, these terms are also ignored for the same reasons as above. However, even when the rotating wave approximation is used, non-oscillating interaction terms remain. The shift to the rotating coordinate system and the rotating wave approximation are used to focus on the behavior of JPOs over their characteristic time scales, and are standard methods for theoretically treating JPOs.

[0098] Angular frequency ω of the pump of JPOk (k = 1 to 4) ｐ，ｋ must satisfy the condition for the three-body interaction (or four-body interaction) to be stationary. The condition depends on which three JPOs are involved in the three-body interaction, but here we consider the situation where JPO1 (20A), JPO2 (20B), and JPO3 (20C) are involved in the three-body interaction as an example. The condition in this case is: ω p,1 +ω p,2 =ω p,3 +2ω p,g (55).

[0099] The angular frequency ω' of the pump of JPO4(20D) not involved in the three-body interaction p,4 Regarding ω' p,4 -2ω p,g　 (56) is large, and this frequency (=ω' p,4 -2ω p,ｇ ) is set so that the vibration of the pump frequency ω' of JPO4(20D) that is not included in the three-body interaction can be ignored as a fast vibration. p,4 is the angular frequency of the pump in the case of four-body interaction, ω p,4 Change from.

[0100] After applying the above unitary transformation and after rotating wave approximation, the Hamiltonian is expressed as follows:

[0101] (57)

[0102] (58)

[0103] (59)

[0104] (60)

[0105] (61)

[0106] (62)

[0107] (63)

[0108] After unitary transformation, the degree of freedom of JPO is a ｋ and the coupler's degree of freedom a ｇ ＋ Since there is no interaction between ｇ ＋ is H' Ｑ In order to show that JPO not involved in the three-body interaction is JPO4(20D), ４ is written as follows. ４ The value of is -1.

[0109] g （３） is the coefficient of the three-body interaction. There are other interactions besides the three-body interaction, but these are terms that also exist in the case of four-body interactions. In particular, g （４） is the four-body interaction (a ＋ １ a ＋ ２ a ３ a ４ ) coefficient, but the term itself is not a four-body interaction but a nonlinear two-body interaction (a ＋ ｋ a ＋ ｋ aｌ a ｌ )

[0110] (64)

[0111] Coupling coefficient g of three-body interaction （３） is expressed as follows: (65)

[0112] As mentioned above, the coefficient of three-body interaction (coupling coefficient) g （３） is a ratio α of the Josephson energies of the second Josephson junction 12 and the first Josephson junction 11 in the coupler 21 (ratio of the junction sizes of the Josephson junctions); the number n of the first Josephson junctions 11 connected in series in the coupler 21; and the capacitance C of the coupler 21. ｇ the coupling capacitance C of the capacitive coupling between the coupler 21 and each JPO; the resonant angular frequency ω of each JPO and the resonant angular frequency ω of the coupler 21; － , Capacitance C of the shunt-connected capacitor of the JPO Ｊ It can be seen that the amplitude parameter ε of the magnetic field oscillation and other parameters are expressed by the circuit parameters.

[0113] g' in equation (62) is the same as in the case of four-body interaction. ε is the amplitude parameter of the oscillating magnetic field applied to the coupler 21. s ４ As mentioned above, the value of is −1, which indicates that JPO4(20D) is not involved in the three-body interaction. Therefore, equation (65) can be expressed as follows:

[0114] (66)

[0115] From the above equation (66), the coefficient g (3) is the capacitance C Ｊ , C ｇ , C, the factor (67)

[0116] Therefore, in addition to n and α, the capacitance C Ｊ , Cｇ By setting the capacitance value of C, the coupling coefficient g (3) For example, the capacitance C of the capacitor 15 of the coupler 21 can be increased. ｇ By reducing the capacitance C of the coupling capacitors 31A to 31D, the coupling coefficient g of the three-body interaction (3) The denominator of (C ｇ + C) becomes smaller, and g (3) The capacitance C of the capacitor 15 of the coupler 21 becomes large. ｇ The capacitance C of each JPO Ｊ The relationship between these capacitances is as follows: C Ｊ >C ｇ >C (68) can also be used.

[0117] As described above, when operating as a four-body interaction coupling, a DC magnetic field (fixed magnetic field) (=Φ0 / 2) is applied to the loop circuit 10 of the coupler 21. When operating as a three-body interaction coupling, the magnetic field applied to the loop circuit 10 is - Φ ｇ of, - With Φ0 / 2 (=h / (4e)) as the center, the amplitude ε × (Φ 0- / 2π), angular frequency ω p,g Vibrate with. (69)

[0118] In order to oscillate the magnetic field applied to the loop circuit 10 of the coupler 21, the control line 13 inductively coupled to the loop circuit 10 of the coupler 21 is preferably impedance-matched to the transmission line connected to the control line 13.

[0119] The coupler 21 also includes a capacitor 15 of capacitance Cg in parallel with the loop circuit 10. As before, let n>1 and α>0.

[0120] Below, as a method different from the above-mentioned method, conditions for realizing the three-body interaction of JPO without oscillating the magnetic field applied to the coupler 21 will be examined.

[0121] The angular frequency ω of the AC magnetic field applied to the SQUIDs (201A to 201D) of each JPO (20A to 20D) ｐ，ｉ (i = 1 to 4) satisfies the following conditions: ω p,1 + ω p,2 = ω p,3 + ω p,4 (70)

[0122] By satisfying the conditional expression (69) (condition for four-body interaction), the strength of the four-body interaction in the rotating coordinate system after the unitary transformation does not oscillate with time but becomes stationary.

[0123] To realize the three-body interaction, for example, in the three-body interaction of JPO1 (20A), JPO2 (20B), and JPO3 (20C), the following condition can be considered as corresponding to equation (70): ω p,1 + ω p,2 = ω p,3 (71)

[0124] By satisfying the conditional expression (71), the strength of the three-body interaction in the rotating coordinate system after the unitary transformation does not oscillate over time but becomes stationary. To satisfy this condition, the angular frequency ω ｐ，３ Therefore, it is necessary to change the pump frequency of JPO3(20C) significantly. For example, if the pump frequency of JPO3(20C) is changed to the angular frequency ω ｐ，３ The pump frequency must be approximately twice the resonant angular frequency of the JPO. Therefore, if the pump frequency of the JPO3(20C) is doubled compared to the case of four-body interaction, the resonant angular frequency of the JPO3(20C) will also change significantly. However, a large change in the resonant angular frequency of the JPO will increase the difference in resonant angular frequency between the JPO and the coupler 21. The resonant angular frequency ω of each JPO and the resonant angular frequency ω of the coupler 21 － The difference (|ω-ω － When |) is large, the four-body coupling coefficient (described later) g （４） The value of becomes smaller.

[0125] Therefore, it is extremely difficult to realize a three-body interaction by setting the magnetic field applied to the coupler 21 so as to satisfy conditional expression (69) without oscillating. In other words, to realize both a strong four-body interaction and a three-body interaction only by adjusting parameters from the outside, some other device is required to replace expression (69). This other device is the above-mentioned method of the present disclosure.

[0126] According to the present disclosure, when a superconducting quantum circuit in which the first to fourth JPOs operate as a four-body interaction via the coupler 21 is operated as a three-body interaction without changing the circuit structure, the following steps are performed: Oscillate the magnetic field of the coupler 21; and Change the resonant angular frequency of the JPO that does not participate in the three-body interaction. As a prerequisite, when the magnetic field of the coupler 21 is not oscillated, it is assumed that the four-body interaction of the four JPOs is realized, and in particular, equation (69) is satisfied for the pump frequency (four-body interaction operating mode). Under these circumstances, consider the three-body interaction of JPO1 (20A), JPO2 (20B), and JPO3 (20C), and assume that JPO4 (20D) does not participate in this three-body interaction.

[0127] Even when the magnetic field applied to the loop circuit 10 of the coupler 21 is not oscillated, the three-body interaction of the three JPOs exists. However, since JPO4(20D) does not participate in the three-body interaction, the interaction coefficient oscillates at the resonant angular frequency of JPO4(20D) and is not steady. Therefore, when the magnetic field applied to the loop circuit 10 of the coupler 21 is oscillated at the pump angular frequency ω of JPO4(20D), ４ The oscillation of the magnetic field applied to the loop circuit 10 of the coupler 21 leads to oscillation of the three-body interaction coefficient, and under the rotating wave approximation, the oscillation of the three-body interaction itself is canceled out, resulting in the realization of a steady three-body interaction. p,1 + ω p,2 = ω p,3 + 2ω p,g (72)

[0128] When equation (72) is made to correspond to equation (70), the pump angular frequency ω of JPO4(20D) in equation (70) is ｐ，４(approximately twice the resonant angular frequency) is replaced by the angular frequency 2ω of the magnetic field oscillation applied to the loop circuit 10 of the coupler 21. ｐ，ｇ In addition, equation (72) adds 2ω to the right side of equation (71). ｐ，ｇ In other words, instead of the resonant angular frequency of JPO4 (20D), the magnetic field is oscillated to compensate for the frequency mismatch between the three JPO1 (20A) to JPO3 (20C).

[0129] In order to realize only three-body interactions and not generate steady four-body interactions when the magnetic field applied to the loop circuit 10 of the coupler 21 is oscillated, the resonant angular frequency of the JPO (here, JPO4(20D)) that does not participate in the three-body interaction is changed so that the conditional expression (69) for the four-body interaction does not hold.

[0130] As described above, when a DC magnetic field is applied to the loop circuit 10 of the coupler 21, if the angular frequency is set to satisfy equation (69), a four-body interaction is realized, and when an AC magnetic field is applied so that equation (70) holds, a three-body interaction is realized. This switching is possible by simply setting parameters externally, without changing the circuit structure.

[0131] In the rotating coordinate system, the three-body interaction term (a １ ＋ a ２ ＋ a ３ ) itself is the angular frequency (ω ｐ，１ +ω ｐ，２ -ω ｐ，３ ) / 2. Therefore, it would be ignored if left as is. However, for the following reason, the coefficient multiplied by the three-body interaction term oscillates due to the influence of the oscillating magnetic field of the coupler 21, and the oscillations are canceled out overall.

[0132] Coefficient g of the three-body interaction term （３） contains the coefficient of the cubic term of the potential function of the coupler 21. When the magnetic field applied to the loop circuit 10 of the coupler 21 has an angular frequency ω ｐ，ｇ When the frequency is oscillating at ω, the coefficient of this third-order term also becomes ｐ，ｇ This means that the three-body interaction term, including the coefficient of the cubic term, oscillates at the angular frequency (ω p,1+ω p,2 -ω p,3 ) / 2-ω p,g　　　 (73) will vibrate.

[0133] angular frequency ω ｐ，１ , ω ｐ，２ , ω ｐ，３ , ω ｐ，ｇ satisfies the conditional expression (72), the frequency of oscillation of the three-body interaction term becomes 0 in the rotating coordinate system, and the three-body interaction becomes stationary.

[0134] Next, an example of the effect of adjusting n and α will be described based on the following specific circuit parameter settings.

[0135]

[0136] The parameters of the Josephson junction are adjusted so that the above frequency is realized. The parameter ε of the amplitude (ε×(Φ0 / (2π)) of the oscillating magnetic field of the coupler 21 is set to 0.01. The coefficient g of the three-body interaction （３） The effect of adjusting n and α is evaluated by the absolute value of . The reason for this is as follows.

[0137] The above g （３） According to the formula, s ｉ The value of (s １ =s ２ = 1, s ３ =s ４ =-1), g （３） However, by adjusting other parameters, the value of g （３） This means that the four-body interaction coefficient g （４） This is the same as changing the sign of g. （３） It is not essential that the sign of g （３） 4 shows the relationship between the absolute value of E and the number of first Josephson junctions 11 connected in series in the loop circuit 10, n, in the above setting, which is 1, 2, 3, 5, and 10. Ｊ１ = E Ｊｇ , E Ｊ２ = αE Ｊｇ (where 0<α<1)) when only g （３）As shown in FIG. 4, in the region where the value of α is large, especially as α approaches α≈1 / n, the absolute value of g （３） The absolute value of increases sharply.

[0138] Furthermore, with the same circuit parameters, the strength of the four-body interaction g when the magnetic field of the coupler 21 is not oscillated is （４） and g （３） A comparison of these is shown in Figure 5 for the case of n = 2. Below, we will give an overview of the four-body interaction coefficient g(4).

[0139] The quantized Hamiltonian HQ is given by equation (40) above and is reproduced below.

[0140] HJPO,i is the Hamiltonian of each JPOi (i = 1, 2, 3, 4) and is given by the above equation (42). ｃｏｕｐｌｅｒ is the Hamiltonian of the coupler 21 and is given by the following equation (74). (74)

[0141] By applying a unitary transformation and shifting to a rotating coordinate system, the Hamiltonian can be expressed by the following equation (75). (75)

[0142] In formula (75), H ’ ＪＰＯ，ｉ (i = 1, 2, 3, 4) is the Hamiltonian of JPO1 (20A) to JPO4 (20D).

[0143] H ’ ｃｏｕｐｌｅｒ is the Hamiltonian of the coupler 21.

[0144] Coupling coefficient g of four-body interaction （４） is given by the following equation (76). (76)

[0145] In equation (76), the resonant angular frequency ω of each JPO is given by the following equation (77), which is the same as equation (43) above. (77)

[0146] In equation (76), ω －is the resonant angular frequency of the coupler 21 (boson operator a ｇ－ (resonant angular frequency corresponding to ) and is given by the following equation (78). (78)

[0147] In formula (78), E ’ ｃｇ is the combined capacitance: C ｇ +C charging energy, which is given by the following equation (79): (79)

[0148] In equation (78), E Ｊg （２） is given by the following equation (80). (80) Therefore, the resonant angular frequency ω_ of the coupler 21 in equation (78) can be expressed by the following equation (81).

[0149] (81)

[0150] Resonant angular frequency ω of coupler 21 － depends on n and α, but the resonant angular frequency ω of each JPO does not depend on n and α. By changing n and α, the resonant angular frequency ω of the coupler 21 can be － When the value of is far from the resonant angular frequency ω of each JPO, the coupling coefficient g （４） becomes smaller. ω － The value of must be adjusted by parameters other than n and α. This is because the critical current I of each Josephson junction in the coupler 21 ｃｇ This can be achieved by adjusting the

[0151] Coefficient g （４） is the capacitance C Ｊ , C ｇ , C, the factor (82)

[0152] Therefore, in addition to the circuit parameters n and α in the coupler 21, the capacitance C Ｊ , C ｇ , by setting the capacitance value of C, the coupling coefficient g of the four-body interaction （４）For example, the capacitance C of the capacitor 15 of the coupler 21 can be increased. ｇ By reducing the capacitance C of the coupling capacitors 31A to 31D, the coupling coefficient g of the four-body interaction （４） The denominator of C ｇ +C becomes smaller, and g （４） The capacitance Cg of the capacitor 15 of the coupler 21 is set to the capacitance C of each JPO. Ｊ The relationship between these capacitances is as follows, similar to the above equation (68): C Ｊ >C ｇ >C (83) may be satisfied.

[0153] Referring to Figures 4 and 5, g （４） and g （３） The parameter values ​​used in the calculation of are the same except for ε, a parameter specific to the three-body interaction. In the region where α is greater than 0.2, g （４） and g （３） The absolute values ​​of each are roughly the same.

[0154] As described above, the circuit structure exemplified in this disclosure allows switching between four-body interaction and three-body interaction operation for JPO1 to JPO4 (20A to 20D) in response to external parameter settings, without changing the circuit structure of the JPO and coupler 21. Whether four-body interaction or three-body interaction is realized primarily depends on whether the magnetic field applied to the parallel circuit portion of the coupler is constant or oscillating. By adjusting the parameters n and α included in the circuit, particularly by setting α ≈ 1 / n within the range of α < 1 / n, the absolute values ​​of the four-body interaction coefficient and the three-body interaction coefficient can be increased.

[0155] 2B, the loop circuit 10 of the coupler 21 shown in Fig. 1 may have, for example, n first Josephson junctions 11-1 to 11-n as 0 junctions and a second Josephson junction 12 as a π junction. For an array of n first Josephson junctions 11-1 to 11-n connected in series, the phase difference between both ends of the array (between nodes n1 and n2) may be φ １ , the phase difference at the second Josephson junction 12 is φ ２In this case, an extra phase difference π occurs in comparison with the phase difference φ2−φ1 when the light goes around the loop circuit 10, and the following holds true: (84)

[0156] Therefore, the potential energy of the second Josephson junction 12 is (85) and the potential energy V(φ １ ) is the same as the above-mentioned formula (10). That is, when the loop circuit 10 has a configuration including an odd number of π junctions, the magnetic flux Φ g Without applying magnetic flux Φ g =0), the loop circuit 10 is passed through the magnetic flux Φ ０ / 2 (or -Φ ０ / 2) (where Φ ０ (=h / (2e)) is a magnetic flux quantum). Therefore, when the loop circuit 10 has a configuration including an odd number of π junctions, a DC bias source is not required.

[0157] Alternatively, the coupler 21 shown in FIG. 1 may be configured by adding an odd number of π-junction Josephson junctions (phase difference = π) to the loop circuit 10. That is, the coupler 21 shown in FIG. 1 may have the configuration shown in FIG. 6A or 6B, for example. Referring to FIG. 6A, the coupler 21 may have a configuration including n first Josephson junctions 11-1 to 11-n with 0 junctions connected in series between nodes n1 and n2, a second Josephson junction 12 with 0 junctions connected in series between nodes n1 and n2, and (2k+1) third Josephson junctions 12π-1 to 12π-(2k+1) with π junctions (k is a predetermined integer equal to or greater than 0). The loop circuit 10 includes (n+1)+(2k+1)=n+2k+2 Josephson junctions within the loop. Here, the critical current values ​​(Josephson energies) of the third Josephson junctions 12π-1 to 12π-(2k+1) are assumed to be large, and the phase difference between each is approximately π. For simplicity, the case where there is one third Josephson junction (denoted as 12π) will be explained. The energy of the third Josephson junction 12π is -E Ｊπ cos(φ π+π) = E Ｊπ cos(φ π ) and φ π In the case of a normal Josephson junction, the phase difference φ fluctuates around a value that reduces the energy of the entire circuit (for example, FIG. 6A). However, the Josephson energy E of the third Josephson junction 12π Ｊπ Since the phase difference φ is large, reducing the energy of the third Josephson junction 12π itself reduces the energy of the entire circuit. π = π, and the fluctuation can be ignored. The phase difference between node n1 and node n2 is φ １ Then, the phase difference in each of the first Josephson junctions 11-1 to 11-n is φ １ / n, and the phase difference φ of the second Josephson junction 12 of the zero junction ２ Between (86) holds. (87) This means that the external magnetic flux Φ in Eq. ｇ The magnetic flux quantum Φ ０ (=h / (2e): magnetic flux quantum) / 2 (Φ ｇ =Φ ０ / 2) (φ １ -φ ２ (The sign of the symbol is not essential.) Alternatively, an odd number of third Josephson junctions 12π may be connected in series to n first Josephson junctions 11. For simplicity, FIG. 6B shows a configuration in which one third Josephson junction 12π is connected in series to n first Josephson junctions 11. In FIG. 6B, the following holds true regarding the phase difference of the Josephson junctions in the loop circuit 10: (88) (89) Equation (89) is the external magnetic flux Φ in equation (1). ｇ The magnetic flux quantum Φ ０ 1 / 2 of (Φ ｇ =Φ ０ In either case, the magnetic flux Φ ｇWithout applying an external magnetic flux Φ ｇ =0), the loop circuit 10 is connected to the magnetic flux Φ ０ / 2 (or -Φ ０ / 2) (Φ ０ (=h / (2e)) is a magnetic flux quantum). The third Josephson junctions 12π may be inserted separately in the loop circuit 10, instead of being connected in series as a single (2k+1) piece. For example, a configuration may be provided in which {(2k+1)-m} third Josephson junctions are connected in series with n first Josephson junctions 11, and m third Josephson junctions are connected in series with the second Josephson junctions 12 (where equation (87) or (89) holds).

[0158] FIG. 7 shows a non-limiting example of the pattern of the coupler 21 on a wiring layer on a substrate. The JPO1 to JPO4 bodies are also formed on the same wiring layer, but their patterns are omitted. The coupler 21 is surrounded by a ground pattern (ground plane) 40. Although not particularly limited, the coupler connection sections 24A to 24D of JPO1 to JPO4 are surrounded by ground patterns (ground planes) 40 on both sides with gaps between them, and the JPO1 to JPO4 bodies are also surrounded by the ground pattern (ground plane) 40. As shown schematically in FIG. 7 , the coupler 21 is spaced from the edge of the ground pattern (ground plane) 40 by a gap of, for example, about the size of the coupler 21 (on the order of a fraction to several times that size). When the coupler 21 is on the order of 10 to 100 μm (micrometers) (tens to hundreds of μm), the gap spacing may be approximately this order. In FIG. 7, reference numeral 41 denotes a region where no ground pattern is provided and the substrate is exposed.

[0159] 7, the first electrode 16 of the coupler 21 has a generally trapezoidal planar shape rotated approximately 45 degrees counterclockwise relative to the horizontal direction of the drawing. The first and second opposing portions 17A and 17B of the first electrode 16 extend from the hypotenuse (leg) of the trapezoid toward the left and top of the drawing toward the coupler connection portions 24A and 24B of JPO1 and JPO2, respectively. The second electrode 18 has a generally inverted trapezoidal planar shape rotated 180 degrees from the first electrode 16, and the third and fourth opposing portions 19A and 19B of the second electrode 18 extend from the hypotenuse toward the right and bottom of the drawing toward the coupler connection portions 24C and 24D of JPO3 and JPO4, respectively. The first electrode 16 and the second electrode 18 are disposed with their trapezoidal bases facing each other, and the combined planar shape of the main body, excluding the facing portion, is approximately hexagonal. The first electrode 16 has a protrusion 16C protruding downward in the figure near the intersection of one end of the lower base and the oblique side, and the second electrode 18 has a cutout 18C near the intersection of one end of the lower base and the oblique side, cut out so as to be parallel to the protrusion 16C of the first electrode 16. A loop circuit 10 is formed between the protrusion 16C near the intersection of one end of the lower base of the first electrode 16 and the cutout 18C near the intersection of one end of the lower base of the second electrode 18 and the oblique side (note that the first Josephson junctions 11-1 to 11-n and the second Josephson junction 12 in FIG. 9 are not shown due to the difference in size between the loop circuit 10 and the first and second electrodes 16 and 18).

[0160] In the loop circuit 10 of the coupler 21, for example, if the second Josephson junction 12 is a π junction and the remaining n first Josephson junctions 11-1 to 11-n are 0 junctions, when the loop circuit 10 is operated by four-body interaction, the magnetic flux Φ ０ Even if you do not give / 2, the phase difference around the loop circuit is on average ±Φ ０ / 2 × (2k + 1) (where Φ ０ (=h / (2e)) is the magnetic flux quantum: h is Planck's constant, and e is the elementary charge).

[0161] Alternatively, the loop circuit 10 of the coupler 21 may be configured to include n (n is a predetermined positive integer) first Josephson junctions 11-1 to 11-n with zero junctions connected in series, a second Josephson junction 12 with zero junctions connected in parallel to the n first Josephson junctions 11-1 to 11-n, and a third Josephson junction 12π with a total of an odd number of π junctions connected in series to the n first Josephson junctions 11-1 to 11-n and / or the second Josephson junction 12 (FIGS. 6A and 6B).

[0162] In the loop circuit 10 of the coupler 21, when n first Josephson junctions 11-1 to 11-n and the second Josephson junction 12 are all zero junctions, and when the loop circuit 10 is operated by four-body interaction, the magnetic flux Φ ０ / 2, a direct current supplied from a current control unit (DC bias source 404B in FIG. 9 ) flows through control line 13, which generates a magnetic field (magnetic flux) that penetrates loop circuit 10. Control line 13 is configured, for example, as a line with ground patterns 40 arranged on both sides of its length with gaps between them, and its ends function as magnetic field generating unit 14 in FIG. 1 and are connected to the ground (ground pattern 40) near loop circuit 10. Therefore, near loop circuit 10, there is a portion 30 that causes ground pattern 40 to jut inward and move closer to loop circuit 10.

[0163] When operating using four-body interactions, the control line 13 passes an AC (microwave) current supplied from a current control unit (microwave signal source 403B in Figure 9) not shown, and a DC current supplied from a current control unit (DC bias source 404B in Figure 9) not shown, thereby oscillating the magnetic field passing through the loop circuit 10.

[0164] In the loop circuit 10 of the coupler 21, (a) a configuration in which the first Josephson junctions 11-1 to 11-n and the second Josephson junction 12 are all 0 junctions, (b) a configuration in which the second Josephson junction 12 is a π junction and the remaining n first Josephson junctions 11-1 to 11-n are 0 junctions, (c) In any of the configurations (FIGS. 6A and 6B) including n first Josephson junctions 11-1 to 11-n with 0 junctions, a second Josephson junction 12 with 0 junctions connected in parallel to the n first Josephson junctions 11-1 to 11-n with 0 junctions, n (n is a predetermined positive integer) first Josephson junctions 11-1 to 11-n with 0 junctions connected in series, a second Josephson junction 12 with 0 junctions connected in parallel to the n first Josephson junctions 11-1 to 11-n with 0 junctions, and a third Josephson junction 12π with a total of an odd number of π junctions connected in series to the n first Josephson junctions 11-1 to 11-n and / or the second Josephson junction 12, when operated by three-body interaction, the control line 13 passes an AC current (microwave current) supplied from a current control unit (not shown) to generate a magnetic flux Φ passing through the loop circuit 10. The magnetic flux Φ passing through the loop circuit 10 and generated by the magnetic field generating unit 14 oscillates at the same angular frequency as the resonant angular frequency of one of JPO1 (20A) to JPO4 (20D) that does not participate in the three-body interaction.

[0165] 7, in order to efficiently apply magnetic flux by inductive coupling with the control line 13 (line), the distance between the ground pattern 40 and only the first electrode 16 and the second electrode 18, which are in the vicinity of the Josephson junction loop circuit 10, is reduced, and the control line 13 is formed in the vicinity of the loop circuit 10, thereby making it possible to apply magnetic flux Φ from very close to the loop circuit 10. As described above, the ground pattern 40 is basically spaced apart from the first and second electrodes 16 and 18, except for the portion 30 that brings it close to the loop circuit 10.

[0166] 7 shows an example in which the control line 13 and the magnetic field generator 14 are arranged on the same wiring layer as the coupler 21, but it goes without saying that the present invention is not limited to this configuration. For example, in a wiring board (interposer) (not shown) on which a quantum chip including the coupler 21 is flip-chip mounted via bumps, the control line 13 and the magnetic field generator 14 may be provided on the surface on which the quantum chip is mounted, at a position facing the loop circuit 10 of the coupler 21 or in the vicinity thereof.

[0167] In the coupler 21 having the configuration shown in FIG. 7, the capacitance C Ｊ , the capacitance C of the capacitor (15 in FIG. 1) of the coupler 21 ｇ , the capacitance C of the coupling capacitors (31A-31D in FIG. 1) between the coupler connection parts 24A-24D of JPO1 (20A) to JPO4 (20D) and the opposing parts 17A, 17B, 19A, and 19B of the coupler 21 is: C Ｊ >C ｇ >C.

[0168] The electrode structure of the coupler 21 in FIG. 7 may be such that L-shaped and inverted L-shaped electrodes are arranged opposite each other to form the first electrode 16 and the second electrode 18, the first electrode 16 and the second electrode 18 having a comb-teeth-like nested structure extending opposite each other, and one of the gaps between the opposing ends of the L-shaped and inverted L-shaped sides of the first electrode 16 and the second electrode 18 is provided with a parallel circuit of n first Josephson junctions 11 and n second Josephson junctions 12 connected in series in the loop circuit 10 in FIG. 2(B).

[0169] 8 and 9 are diagrams illustrating an example of the device configuration of the present disclosure. This diagram illustrates an example of the connection between the JPO and measurement electronics external to the refrigerator. FIG. 8 illustrates an example of the connection between the IO terminal and pump terminal, which connect the IO line and control line (pump line) of the JPO, and measurement electronics external to the refrigerator. One end of the IO line is connected to the JPO via a coupling capacitor Cc, and the other end is connected to a circulator 408 via the IO terminal. A signal from a signal source 401A external to the dilution refrigerator is transmitted via a coaxial cable or the like wired inside the dilution refrigerator, attenuated stepwise by attenuators (Att.) 405, 406, and 407 installed at each temperature stage, transmitted to the IO terminal via the circulator 408, and input to JPO1 (20A in FIG. 1 ). The reflected signal of the output signal wave / input signal wave from JPO1 (20A in Figure 1) is transmitted from the IO terminal via a circulator 408, a low pass filter (LPF) 412, a band pass filter (BPF) 411, an isolator 410, a high electron mobility transistor (HEMT) amplifier 409, etc., to an amplifier 418 outside the dilution refrigerator, where it is further amplified and transmitted to a signal receiver 402A. A pump signal (microwave signal) from a microwave signal source 403A that generates the pump signal is transmitted through a coaxial cable wired inside the dilution refrigerator, and is attenuated stepwise by attenuators (Att.) 413A, 414A, and 415A installed at each temperature stage, and then input to a bias T circuit 416A. A DC (Direct Current) signal from the DC bias source 404A is transmitted through a transmission line (twisted pair) or the like wired inside the dilution refrigerator and input to a bias T circuit 416A via an LPF 417A. In the bias T circuit 416A, a junction point between a capacitor C3, one end of which receives microwaves from the microwave signal source 403A, and an inductor L3 (choke coil), one end of which is connected to the output of the LPF 417A, is connected to a pump terminal.The bias-T circuit 416A combines a capacitor C3, through which only high-frequency current flows, with an inductor L3 (choke coil), which passes DC or currents at frequencies lower than a predetermined frequency and blocks currents higher than the predetermined frequency, to superimpose a DC signal on the RF signal and supply it to a control line (pump line). That is, by supplying a DC bias signal that DC-flux biases the SQUID of the JPO and a pump signal with an angular frequency approximately twice the resonant angular frequency ω of the SQUID resonator from a microwave signal source 403A to the control line (pump line), the JPO can be parametrically oscillated at the angular frequency ω. The JPO parametrically oscillates when a pump signal of sufficient intensity (angular frequency ≈ 2ω) exceeding a threshold is applied. Varying the strength of the pump signal (effective value or power of the DC bias current or microwave current) and / or the microwave frequency also changes the strength (strength of the magnetic field H) and / or frequency of the magnetic field (magnetic field) generated by the inductor L1 (magnetic field generating unit). Therefore, the strength and / or frequency of the magnetic field from the inductor L1 of each JPO controls the parametric oscillation of each JPO.

[0170] 8 shows only JPO1 (20A in FIG. 1) as the JPO connected to coupler 21, but the other JPOs are also connected to signal sources, receivers, etc. in the same configuration as JPO1. In the three-body interaction operation mode, controller 50 sets the frequency of the pump signal from microwave signal source 403A connected to a JPO not participating in the three-body interaction (e.g., JPO4) to a value different from the frequency in the four-body interaction. In conjunction with a change in the pump frequency, the signal source that supplies a signal to a JPO not participating in the three-body interaction (e.g., JPO4) and the receiver that receives a readout signal from a JPO not participating in the three-body interaction (e.g., JPO4) may be changed.

[0171] 9 is a diagram illustrating an example of the connection between the IO terminal and control terminal, which connect the IO line and control line of coupler 21, and measurement electronics external to the refrigerator. Referring to Fig. 9, when operating with four-body interactions, controller 50 deactivates microwave signal source 403B (output-off state or power-off state), and a DC signal (DC current) from DC bias source 404B external to the dilution refrigerator is supplied to the pump terminal via low-pass filter 417B and bias T circuit 416B, and is then supplied to control line 13, one end of which is grounded. When operating with three-body interactions, controller 50 activates microwave signal source 403B external to the dilution refrigerator to output a microwave signal. The microwave signal is transmitted through a coaxial cable or the like wired inside the dilution refrigerator, attenuated in stages by attenuators (Att.) 413B, 414B, and 415B installed at each temperature stage, and input to a bias-T circuit 416B. A signal to which a DC signal is added is supplied to a control terminal, and the signal is supplied to one end of inductor L5, one end of which is connected to ground, via a control line 13. Changing the effective value or power of the DC current or microwave current flowing through control line 13 and / or the microwave frequency also changes the strength (strength of magnetic field H) and / or frequency of the magnetic field (magnetic field) generated by inductor L5 (magnetic field generating unit).

[0172] In the loop circuit 10 of the coupler 21, for example, if the n first Josephson junctions 11-1 to 11-n are 0 junctions and the second Josephson junction 12 is a π junction, the DC bias source 404B and the bias T circuit 416B are not required. Also, if the loop circuit 10 of the coupler 21 has the configuration shown in Figure 6(A) or 6(B), the DC bias source 404B and the bias T circuit 416B are not required.

[0173] FIG. 10 is a diagram showing a schematic configuration of a quantum computer 300 using JPOs (20) and couplers 21. The couplers 21 connect four adjacent JPOs (20) to form a unit structure (also called a plaquette). The configuration in FIG. 10 is suitable for a network using the LHZ (Lechner, Hauke, Zoller) method, which is one of the quantum annealing methods. For information on fully connected quantum annealing using the configuration in FIG. 10, see, for example, Non-Patent Document 1.

[0174] It is worth noting that, in FIG. 10, among JPO20A, JPO20B, JPO20C, and JPO20D coupled by four-body interaction, when, for example, JPO20A breaks down or needs to be put into an inoperative state and becomes defective, the magnetic field applied to the loop circuit of coupler 21A is increased by a predetermined amplitude ε(ε(Φ 0- / (2π)): Φ is the magnetic flux quantum), and the pump frequency of JPO 20A, which is removed from the three-body interaction, is set to a value different from the pump frequency when operating with four-body interactions, thereby enabling switching to operation with three-body interactions by JPO 20B, JPO 20C, and JPO 20D via coupler 21A. After JPO 20A is restored, a DC magnetic field is applied to the loop circuit of coupler 21A (not necessary if loop circuit 10 has an odd number of π bonds; the supply of an AC magnetic field is stopped), and a pump frequency that satisfies the conditions for four-body interactions is supplied to JPO 20A, thereby coupling JPO 20A to JPO 20D via coupler 21A through four-body interactions.

[0175] Furthermore, among JPO20A, JPO20B, JPO20C, and JPO20D coupled by four-body interaction, when, for example, JPO20B fails or needs to be put into an inoperative state and becomes missing, the magnetic field applied to the loop circuits of couplers 21A and 21B that share JPO20B is set to a predetermined amplitude ε(ε(Φ 0- / (2π)): Φ is the magnetic flux quantum), and the pump frequency of JPO20B is set to a frequency different from the pump frequency during operation with four-body interactions, thereby enabling switching between operation with three-body interactions using JPO20A, JPO20C, and JPO20D via coupler 21A and operation with three-body interactions using JPO20E, JPO20D, and JPO20H via coupler 21B. After JPO20B is restored, a DC magnetic field is applied to the loop circuit of coupler 21A and coupler 21B (this is not necessary if loop circuit 10 has an odd number of π bonds, and the supply of an AC magnetic field is stopped), and a pump frequency that satisfies the conditions for four-body interaction is supplied to JPO20B, whereby JPO20A, JPO20B, JPO20C, and JPO20D are coupled by four-body interaction via coupler 21A, and JPO20E, JPO20B, JPO20D, and JPO20H are coupled by four-body interaction via coupler 21B. The same applies to the other unit structures (plaquette).

[0176] Although not particularly limited, the superconducting quantum circuit device of the present disclosure may be further noted as follows, for example.

[0177] (Supplementary Note 1) A superconducting quantum circuit device includes first to fourth quantum bits, a loop circuit including a plurality of Josephson junctions, and a coupler coupled to the first to fourth quantum bits, and further includes control means for switching between a first operating mode in which the first to fourth quantum bits perform four-body interactions via the coupler and a second operating mode in which three quantum bits, excluding one quantum bit, of the first to fourth quantum bits perform three-body interactions via the coupler. The control means includes a magnetic field generation unit that generates a magnetic field to be applied to the loop circuit, and a control unit that changes the intensity and / or frequency of the magnetic field.

[0178] (Supplementary Note 2) In the superconducting quantum circuit device of Supplementary Note 1, in the first operation mode, the phase difference circulating around the loop circuit of the coupler satisfies a predetermined condition, and the resonant angular frequencies of the first to fourth quantum bits satisfy a predetermined condition regarding four-body interaction, and in the second operation mode, an AC magnetic field having a frequency corresponding to the resonant angular frequency of one quantum bit is applied to the loop of the coupler, and the resonant angular frequency of the one quantum bit is set to a value that does not satisfy the predetermined condition regarding four-body interaction.

[0179] (Supplementary Note 3) In the superconducting quantum circuit device of Supplementary Note 2, the coupler comprises a capacitor connected in parallel to the loop circuit connected between one end and the other end of the coupler, the loop circuit having: n (n is a positive integer of 2 or more) first Josephson junctions spaced apart from each other and arranged in series; and a second Josephson junction arranged in parallel to the n first Josephson junctions, the junction size of which is smaller than that of the first Josephson junctions; the first and second quantum bits are capacitively coupled to the one end of the coupler, respectively; and the third and fourth quantum bits are capacitively coupled to the other end of the coupler, respectively; and magnitudes of the coupling coefficients of the three-body interaction and the four-body interaction by the coupler can be freely set based on circuit parameters including at least n; and a ratio α (0<α<1) of the Josephson energy of the second Josephson junction to the Josephson energy of the first Josephson junction.

[0180] (Supplementary Note 4) In the superconducting quantum circuit device of Supplementary Note 3, the control unit includes a current control unit that supplies a current to the magnetic field generation unit, and the magnetic field generation unit, in the first operation mode, causes a direct current from the current control unit to flow through the loop circuit of the coupler, and ０ In the second operation mode, an AC current is applied from the current control unit to pass through the loop circuit of the coupler and generate a magnetic flux of ±Φ ０ / 2 (where Φ ０ (=h / (2e)) is the magnetic flux quantum: h is Planck's constant, and e is the elementary charge).

[0181] (Supplementary Note 5) In the superconducting quantum circuit device of Supplementary Note 4, the vibration amplitude of the AC magnetic flux is ε(Φ ０ / (2π)) (ε is 0<ε<<2πΦ （０） ｇ / Φ ０ a predetermined value of Φ （０） ｇ is given by the fixed magnetic flux when operated as a three-body interaction.

[0182] (Supplementary Note 6) In the superconducting quantum circuit device of Supplementary Note 4, the bias line of the magnetic field generating unit is impedance-matched to the transmission line.

[0183] (Supplementary Note 7) In the superconducting quantum circuit device of Supplementary Note 4, in the second operation mode, the control means controls the current control unit to set, by the AC signal, the oscillation angular frequency of the magnetic flux applied from the magnetic field generation unit to the coupler to a resonant angular frequency of one of the first to fourth quantum bits in the first operation mode when operating with the four-body interaction, change the resonant frequency of the one quantum bit from the resonant angular frequency in the first operation mode when operating with the four-body interaction, make the difference between the resonant frequency of the one quantum bit and the resonant angular frequency of the coupler larger than the difference between the resonant angular frequency of the quantum bits other than the one quantum bit and the resonant angular frequency of the coupler, and the coupler couples three of the first to fourth quantum bits other than the one quantum bit by three-body interaction.

[0184] (Supplementary Note 8) In the superconducting quantum circuit device of any one of Supplementary Notes 3 to 7, in the coupler, α is set to a predetermined value that is smaller than the reciprocal 1 / n of n and close to 1 / n.

[0185] (Supplementary Note 9) In the superconducting quantum circuit device of any one of Supplementary Notes 1 to 7, in the coupler, an odd number (2k+1, k is a predetermined non-negative integer) of the n first Josephson junctions and the n second Josephson junctions in the loop circuit form π junctions, and the remaining junctions are 0 junctions. The phase difference when going around the loop circuit is ±π×(2k+1). Even if the magnetic flux passing through the loop circuit oscillates with an average value of 0, the loop circuit has an average value of ±Φ ０ / 2 × (2k + 1) (where Φ ０ (=h / (2e)) is the magnetic flux quantum: h is Planck's constant, and e is the elementary charge).

[0186] (Supplementary Note 10) In the superconducting quantum circuit device of any of Supplements 1 to 7, in the loop circuit of the coupler, the n first Josephson junctions and the second Josephson junctions are made of Josephson junctions with 0 junctions, and the device comprises an odd number of third Josephson junctions with π junctions connected in series to the n first Josephson junctions and / or the second Josephson junctions, and the third Josephson junctions have Josephson energy larger than those of the first Josephson junctions and the second Josephson junctions and have a phase difference of π.

[0187] (Supplementary Note 11) In the superconducting quantum circuit device of Supplementary Note 3, the loop circuit of the coupler comprises a first electrode and a second electrode arranged opposite each other and spaced apart from a ground pattern in a region surrounded by the ground pattern in a wiring layer on a substrate, the n (n is a positive integer of 2 or more) first Josephson junctions and the n second Josephson junctions are respectively arranged in parallel between the first electrode and the second electrode, the first electrode comprises first and second opposing portions extending from a position of the first electrode different from the side opposing the second electrode toward the first and second quantum bits, and the ends of the first electrode are respectively opposed to and capacitively coupled with ends of the coupler connection portions of the first and second quantum bits, and the second electrode comprises The second electrode has third and fourth opposing portions that extend from a position different from the side of the second electrode facing the first electrode toward the third and fourth quantum bits, and the ends of the second electrode face the ends of the coupler connection portions of the third and fourth quantum bits, respectively, and are capacitively coupled.

[0188] (Supplementary Note 12) In the superconducting quantum circuit device of any one of Supplements 1 to 11, each of the first to fourth quantum bits includes a Josephson parametric oscillator, the Josephson parametric oscillator having: a SQUID (superconducting quantum interference device) having two Josephson junctions at both ends of a crossing between a first superconducting line and a second superconducting line that form a loop; a capacitor connected in parallel to the SQUID; and a line that is inductively coupled to the SQUID and generates a magnetic flux that penetrates the loop of the SQUID; one of the first superconducting line and the second superconducting line of the SQUID is set to ground potential, and the other of the first superconducting line and the second superconducting line of the SQUID is connected to the coupler connection part, and parametric oscillation occurs in accordance with a microwave current supplied to the line.

[0189] (Supplementary Note 13) In the superconducting quantum circuit device of Supplementary Note 12, the circuit parameters that define the coupling coefficients of the four-body interaction include, in addition to α and n, a capacitance value C of the capacitive coupling between the coupler connection parts of the first to fourth quantum bits and each of the first to fourth opposing parts of the coupler, and a capacitance value C of the capacitor connected in parallel to the SQUID of each of the first to fourth quantum bits. Ｊ , the value C of the capacitance between the first and second electrodes of the coupler ｇ The relationship between these capacitances is as follows: C Ｊ >C ｇ >It is set to C.

[0190] (Supplementary Note 14) In the superconducting quantum circuit device of Supplementary Note 13, the coupling coefficient of the three-body interaction is: the α and the n; a capacitance value C of the capacitive coupling between the coupler connection part of the first to fourth quantum bits and each of the first to fourth opposing parts of the coupler; and a capacitance value C of the capacitor connected in parallel to the loop circuit of each of the first to fourth quantum bits. Ｊ , the value C of the capacitance between the first and second electrodes of the coupler ｇ , the resonant angular frequency ω of the coupler and the resonant angular frequency ω of each quantum bit, the amplitude ε(Φ ０ / (2π)) (where Φ ０ (=h / (2e)) is the magnetic flux quantum; h is Planck's constant, and e is the elementary charge) It is expressed as:

[0191] (Supplementary Note 15) In the superconducting quantum circuit device of any one of Supplementary Notes 1 to 14, a quantum computer is configured having, as unit structures, the first to fourth quantum bits that perform Josephson parametric oscillation and the coupler.

[0192] (Supplementary Note 16) The superconducting quantum circuit device of Supplementary Note 15 comprises a plurality of the unit structures, and the unit structures constitute a quantum computer in which at least one of the first to fourth quantum bits constituting the unit structures is shared with one or more other unit structures.

[0193] (Supplementary Note 17) A method for controlling a superconducting quantum circuit comprising first to fourth quantum bits and a loop circuit including a plurality of Josephson junctions and a coupler coupled to the first to fourth quantum bits, the method having a first operating mode in which the first to fourth quantum bits perform four-body interactions via the coupler, and a second operating mode in which three quantum bits, excluding one quantum bit, of the first to fourth quantum bits perform three-body interactions via the coupler, by applying a magnetic field to the loop circuit and changing the strength and / or frequency of the magnetic field, switches between the first operating mode in which the circuit operates using the four-body interaction and the second operating mode in which the circuit operates using the three-body interaction.

[0194] (Supplementary Note 18) In the method for controlling a superconducting quantum circuit of Supplementary Note 17, in the first operation mode, the phase difference circulating around the loop of the coupler satisfies a predetermined condition, and the resonant angular frequencies of the first to fourth quantum bits are set to satisfy a predetermined condition regarding the four-body interaction, so that the first to fourth quantum bits perform the four-body interaction via the coupler; and in the second operation mode, an AC magnetic field having a frequency corresponding to the resonant angular frequency of one of the first to fourth quantum bits is applied to the loop of the coupler, and the resonant angular frequency of the one quantum bit is set to a value other than the value that satisfies the predetermined condition regarding the four-body interaction, so that three quantum bits excluding the one quantum bit among the first to fourth quantum bits perform three-body interaction via the coupler; and the first operation mode, in which the superconducting quantum circuit operates using four-body interaction, and the second operation mode, in which the superconducting quantum circuit operates using three-body interaction, can be freely switched between without changing the circuit structure of the superconducting quantum circuit itself.

[0195] [Reference 1] Yufeng Ye, et. al., "Engineering Purely Nonlinear Coupling between Superconducting Qubits Using a Quarton", PHYSICAL REVIEW LETTERS 127, 050502 (2021) [Reference 2] Uri Vool, et. al., "Introduction to Quantum Electromagnetic Circuits", International Journal of Circuit Theory and Applications 45, 897 (2016)

[0196] The disclosures of Non-Patent Documents 1 and 2 and References 1 and 2 are incorporated herein by reference. Modifications and adjustments of the embodiments and examples are possible within the scope of the entire disclosure (including the claims) of this disclosure, and further based on its basic technical concept. Furthermore, various combinations and selections of the various disclosed elements (including each element of each appendix, each element of each example, each element of each drawing, etc.) are possible within the scope of the claims of this disclosure. In other words, this disclosure naturally includes various modifications and alterations that a person skilled in the art would be able to make in accordance with the entire disclosure, including the claims, and the technical concept.

[0197] 1 Superconducting quantum circuit 10 Loop circuit (nonlinear element) 11, 11-1 to 11-n First Josephson junction 12 Second Josephson junction 12π, 12π-1 to 12π-(2k+1) Third Josephson junction 13 Control line 14 Magnetic field generating unit 15 Capacitor 16 Electrode (first electrode) 16C Protrusion 17A, 17B First and second opposing portions 18 Electrode (second electrode) 18C Cut portion 19A, 19B Third and fourth opposing portions 20A to 20D Superconducting quantum bit (JPO) 21 Coupler 23A to 23D Control line (pump line) 24A to 24D Coupler connection portion 30 Portion (ground pattern protruding portion) 31A to 31D Capacitor (coupling capacitor) 40 Ground (GND) pattern (ground plane) 41 Surface of substrate 50 Controller 101-1 to 101-n Superconducting lines 102-1, 102-2 Superconducting lines 103, 104 Superconducting lines 201A, 201B, 201C, 201D First Josephson junction 202A, 202B, 202C, 202D Second Josephson junction 203A, 203B, 203C, 203D First superconducting section 204A, 204B, 204C, 204D Second superconducting section 206A, 206B, 206C, 206D Capacitors 207A, 207B, 207C, 207D Magnetic field generating section 300 Quantum computer 401A Signal source 402A Signal receiver 403A, 403B Microwave signal source 404A, 404B DC bias source 405, 406, 407, 413A, 413B, 414A, 414B, 415A, 415B Attenuator 408 Circulator 409 HEMT 410 Isolator 411 Band pass filter 412, 417A, 417B Low pass filter 416A, 416B Bias T circuit 418 Amplifier

Claims

1. A superconducting quantum circuit device comprising: first to fourth qubits; a loop circuit including a plurality of Josephson junctions; and a coupler coupled to the first to fourth qubits, wherein the first to fourth qubits perform a four-body interaction via the coupler in a first operation mode, and three qubits excluding one qubit among the first to fourth qubits perform a three-body interaction via the coupler in a second operation mode, and further comprising control means for switching between the first and second operation modes, the control means including a magnetic field generating unit for generating a magnetic field applied to the loop circuit, and a control unit for changing the intensity and / or frequency of the magnetic field.

2. The superconducting quantum circuit device according to claim 1, wherein in the first operation mode, the control means is configured such that the phase difference around the loop circuit of the coupler satisfies a predetermined condition, and the resonance angular frequencies of the first to fourth qubits satisfy a predetermined condition related to the four-body interaction, and in the second operation mode, an alternating magnetic field having a frequency corresponding to the resonance angular frequency of the one qubit is applied to the loop of the coupler, and the resonance angular frequency of the one qubit is set to a value different from the value satisfying the predetermined condition related to the four-body interaction.

3. In the coupler, the coupler includes a capacitor connected in parallel to the loop circuit connected between one end and the other end of the coupler, the loop circuit includes n first Josephson junctions (n is a positive integer of 2 or more) arranged in series at intervals from each other, and a second Josephson junction arranged in parallel to the n first Josephson junctions and having a junction size smaller than the junction size of the first Josephson junctions, the first and second qubits are capacitively coupled to the one end of the coupler respectively, the third and fourth qubits are capacitively coupled to the other end of the coupler respectively, and the magnitudes of the coupling coefficients of the three-body interaction and the four-body interaction by the coupler are settable based on circuit parameters including at least the n, and a ratio α (0 < α < 1) of the Josephson energy of the second Josephson junction to the Josephson energy of the first Josephson junction.

4. The control unit includes a current control unit that supplies current to the magnetic field generation unit. In the first operation mode, the magnetic field generation unit passes a direct current from the current control unit through the loop circuit of the coupler to generate a magnetic flux of ±Φ / 2 that penetrates the loop circuit of the coupler. In the second operation mode, the magnetic field generation unit passes an alternating current from the current control unit through the loop circuit of the coupler to generate an alternating magnetic flux that penetrates the loop circuit of the coupler and oscillates with an average of ±Φ / 2 (where Φ(=h / (2e)) is the magnetic flux quantum, h is the Planck constant, and e is the elementary charge). The superconducting quantum circuit device according to claim 3. ０ In the second operation mode, the magnetic field generation unit passes an alternating current from the current control unit through the loop circuit of the coupler to generate an alternating magnetic flux that penetrates the loop circuit of the coupler and oscillates with an average of ±Φ / 2. ０ / 2 (where Φ ０ (=h / (2e)) is the magnetic flux quantum: h is the Planck constant, and e is the elementary charge).

5. The oscillation amplitude of the alternating magnetic flux is ε(Φ ０ / (2π)) (where ε is a predetermined value such that 0 < ε << 2πΦ （０） ｇ / Φ ０ , provided that Φ （０） ｇ is the fixed magnetic flux when operating as a three-body interaction), the superconducting quantum circuit device according to claim 4.

6. The superconducting quantum circuit device according to claim 4, wherein the bias line of the magnetic field generating unit has impedance matching with the transmission line.

7. In the second operation mode, the control means controls the current control unit so that the angular frequency of oscillation of the magnetic flux applied from the magnetic field generating unit to the coupler by the alternating current signal is set to the resonance angular frequency of one of the first to fourth qubits in the first operation mode during operation by the four-body interaction, changes the resonance angular frequency of the one qubit from the resonance angular frequency in the first operation mode during operation by the four-body interaction, makes the difference between the resonance angular frequencies of the one qubit and the resonance angular frequencies of the coupler larger than the difference between the resonance angular frequencies of the qubits other than the one qubit and the resonance angular frequencies of the coupler, and the coupler couples the three qubits other than the one qubit among the first to fourth qubits by three-body interaction. The superconducting quantum circuit device according to claim 4.

8. The superconducting quantum circuit device according to claim 3, wherein in the coupler, α is set to a predetermined value close to 1 / n within a range smaller than 1 / n, the reciprocal of n.

9. In the coupler, among the n first Josephson junctions and the second Josephson junctions of the loop circuit, an odd number (2k + 1, k is a predetermined non - negative integer) form π - junctions, and the rest are 0 - junctions. When the phase difference when going around the loop circuit is set to ±π×(2k + 1), and even if the magnetic flux passing through the loop circuit oscillates with an average value of 0, the loop circuit is biased with a magnetic flux that oscillates at an average of ±Φ ０ / 2×(2k + 1) (where Φ ０ (= h / (2e)) is the magnetic flux quantum: h is the Planck constant, e is the elementary charge)) in a biased state. The superconducting quantum circuit device according to claim 3.

10. In the loop circuit of the coupler, the n first Josephson junctions and the second Josephson junction are composed of 0-junction Josephson junctions, and a total of an odd number of third Josephson junctions of π-junctions connected in series to the n first Josephson junctions and / or the second Josephson junction are provided, and the third Josephson junction has a Josephson energy larger than that of the first Josephson junction and the second Josephson junction and a phase difference of π. The superconducting quantum circuit device according to claim 3.

11. The loop circuit of the coupler includes a first electrode and a second electrode that are disposed opposite to each other and spaced apart from a ground pattern within a region surrounded by the ground pattern in a wiring layer on a substrate. The n (n is a positive integer of 2 or more) first Josephson junctions, the second Josephson junction are respectively arranged in parallel between the first electrode and the second electrode. The first electrode extends from a location different from the side facing the second electrode of the first electrode to the first and second qubit sides respectively, and the ends thereof are provided with first and second opposing portions that capacitively couple to the ends of the coupler connection portions of the first and second qubits respectively. The second electrode extends from a location different from the side facing the first electrode of the second electrode to the third and fourth qubit sides respectively, and the ends thereof are provided with third and fourth opposing portions that capacitively couple to the ends of the coupler connection portions of the third and fourth qubits respectively. The superconducting quantum circuit device according to claim 3.

12. Each of the first to fourth qubits includes a Josephson parametric oscillator. The Josephson parametric oscillator includes a SQUID (superconducting quantum interference device) having two Josephson junctions at both ends where a first superconducting line and a second superconducting line forming a loop intersect, a capacitor connected in parallel to the SQUID, and a line that inductively couples to the SQUID and generates a magnetic flux penetrating the loop of the SQUID. One of the first superconducting line and the second superconducting line of the SQUID is set to a ground potential, the other of the first superconducting line and the second superconducting line of the SQUID is connected to the coupler connection portion, and parametric oscillation occurs according to a microwave current supplied to the line. The superconducting quantum circuit device according to claim 11.

13. In addition to the α and the n, the circuit parameters that define the coupling coefficient of the four-body interaction include the capacitance value C of the capacitive coupling between the coupler connection parts of the first to fourth qubits and each of the first to fourth opposing parts of the coupler, and the capacitance value C of the capacitor connected in parallel to each of the SQUIDs of the first to fourth qubits. Ｊ , the capacitance value C between the first and second electrodes of the coupler. ｇ These include capacitance values, and the magnitude relationship between these capacitances is set such that C Ｊ > C ｇ > C. The superconducting quantum circuit device according to claim 12.

14. The coupling coefficient of the three-body interaction is related to the capacitance value C of the capacitive coupling between α and n, the coupler connection parts of the first to fourth qubits, and each of the first to fourth opposing parts of the coupler, the capacitance value C of the capacitor connected in parallel to the loop circuit of each of the first to fourth qubits Ｊ , the capacitance value C between the first electrode and the second electrode of the coupler ｇ , the resonance angular frequency ω of the coupler － and the resonance angular frequency ω of each qubit, the amplitude ε(Φ ０ / (2π)) of the oscillating magnetic field of the coupler (where Φ ０ (=h / (2e)) is the magnetic flux quantum: h is the Planck constant, e is the elementary charge) with respect to the circuit parameters, The superconducting quantum circuit device according to claim 13, which is represented by 15. A superconducting quantum circuit device, wherein the superconducting quantum circuit device according to any one of claims 1 to 10 constitutes a quantum computer having the first to fourth qubits that perform Josephson parametric oscillation and the coupler as a unit structure.

16. The superconducting quantum circuit device according to claim 15, comprising a plurality of the unit structures, wherein the unit structure shares at least one of the first to fourth qubits constituting the unit structure with one or more other unit structures to form a quantum computer.

17. A control method for a superconducting quantum circuit, comprising the first to fourth qubits and a loop circuit including a plurality of Josephson junctions, and a coupler coupled to the first to fourth qubits, the method comprising: a first operation mode in which the first to fourth qubits perform a four-body interaction via the coupler; and a second operation mode in which three qubits excluding one of the first to fourth qubits perform a three-body interaction via the coupler, and switching between the first operation mode operating in the four-body interaction and the second operation mode operating in the three-body interaction by applying a magnetic field to the loop circuit and changing the intensity and / or frequency of the magnetic field.

18. In the first operation mode, the first to fourth qubits perform the four-body interaction via the coupler by setting the phase difference around the loop of the coupler to satisfy a predetermined condition and setting the resonance angular frequencies of the first to fourth qubits to satisfy a predetermined condition related to the four-body interaction. In the second operation mode, an alternating magnetic field having a frequency corresponding to the resonance angular frequency of one of the first to fourth qubits is applied to the loop of the coupler, and the resonance angular frequency of the one qubit is set to a value different from the value satisfying the predetermined condition related to the four-body interaction, so that three qubits excluding the one qubit among the first to fourth qubits perform a three-body interaction via the coupler. The control method for a superconducting quantum circuit according to claim 17 enables switching between the first operation mode operating in the four-body interaction and the second operation mode operating in the three-body interaction without changing the circuit structure of the superconducting quantum circuit itself.

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